Anti Reflection Coatings
Anti reflection coatings are transmission enhancement coatings which when deposited on the optics will increase the trhoughput into the system, reduce the stray light, and prevent the back surface multiple reflections.
In general, between 4-16% of light is reflected back (lost) by a lens, depending on the material and it's refractive index. The higher the index the more light s reflected and the more noticeable an improvement you get from the AR coating. By adding an AR coating the overall transmission of the lens can be increased by almost 3 to 6%.
The transmission properties of a coating are dependent upon the wavelength of light being used, the substrate's index of refraction, the index of refraction of the coating, the thickness of the coating, and the angle of the incident light.
The coating is designed so that the relative phase shift between the beam reflected at the upper and lower boundary of the thin film is 180°. Destructive interference between the two reflected beams occurs, cancelling both beams before they exit the surface. The optical thickness of the coating must be an odd number of quarter wavelengths (λ/4, where λ is the design wavelength or wavelength being optimized for peak performance), in order to achieve the desired path difference of one half wavelength between the reflected beams, which leads to their cancellation.
SINGLE LAYER AR COATINGS
It is the good choice for the index material substrates like SF4, SF10, SF11 glasses, sapphire etc. The low index 1.38 of MgF2 acts as a perfect impedance matching layer between the high index glass and air.
Coatings : Single layer MgF2;
Performance : R<1.2%
AR COATINGS FOR LASER OPTICS
Antireflection coating on optical components for laser wavelengths is designed with suitable dielectric multilayer to have a low absorption, minimum surface reflection loss with high damage threshold. The designed layers are electron beam deposited under the presence of high energetic ion beam to increase the packing density and stoichiometry and monitored through optical thickness monitor to ensure the close match of the design to achieve the desired transmittance with batch by batch consistency. This advanced deposition technology offers the high resistance to laser damage, making them suitable for high-energy laser usage with minimum transmission loss.
Coatings : 532nm, 633nm and 1064nm ; Performance : R< 0.3 %
BROAD BAND AR COATINGS
Most of the optical systems work for broadband sources. Hence the optical components in the system are needs to be coated with broadband antireflection coating suiting to the source spectrum.
Wavelength : 400-700, 400-900 and 500 – 1100 nm ;
Performance : R< 1 %
AR COATINGS FOR INFRARED OPTICS
Imaging the objects that are beyond the visible region is of the interest in both terrestrial and astronomical applications. Imaging an object in infrared will reveal its physical characteristics and heat signature. Thermal imaging has applications in defense, industrial security, transportation, cancer detection, body scans, and hot-spot detection.
Wavelength : 8 TO 12 micron
Performance : T> 93 %